We have previously demonstrated that Qa-1 dependent CD8+ T cells control the peripheral self-reactive TCR repertoire in EAE mice by selectively down-regulating some but not all MBP reactive T cell clones which have higher growth potential to MBP and enriched in the potentially pathogenic MBP-reactive clones. In recent studies we further demonstrated that Qa-1 dependent CD8+ T cells are biologically involved in the development and maintenance of peripheral tolerance to the self-antigen HEL in HEL transgenic mice. We provide experimental evidence that the strategy employed by the Qa-1 dependent CD8+ T cells to accomplish these tasks in vivo is to selectively down-regulate CD4+ T cell clones that are of intermediate, but not high or low, affinity/avidity responding to HEL. In this application we will extend our studies to the EAE model to further identify the cellular and molecular mechanisms that define the specific interaction between the Qa-1 dependent CD8+ T cells and the self-reactive CD4+ T cells. We will identify the peripheral self- reactive repertoire and the relationship between affinity/avidity and pathogenicity of self-reactive T cells in EAE model to further understand how preferential down regulation of certain affinity/avidity clones by the Qa- 1 dependent CD8+ T cells provides a mechanism to control the pathogenic auto-immunity in the periphery. We will also identify and test Qa-1 binding peptide/s which render the activated T cells susceptible to the down-regulation by the CD8+ T cell thus protect the animals from auto-immune disease. In addition, we will characterize the immune functions of the Qa-1 dependent CD8+ T cells in EAE by identifying the TCR Va and Vp repertoire of the CD8+ T cells and defining the other immunologic functions mediated by CD8+ T cells. In this regard, unlike HEL transgenic mice model system, EAE model is a classical autoimmune disease model which has its unique advantage that HEL transgenic mice model system does not have. Particularly, the major classical auto-immune disease models currently used, such as NOD mice, NZB/NZW mice and B10PL/EAE mice are all Qa-1 a hyplotype. Qa-1 is one of the crucial components of this regulatory pathway, which may lead to the therapeutic application in preventing and treating auto-immune disease. So that it is very important to test the biological function of Qa-1 in Qa-1 strains such as B10PL mice in auto- immune disease models. Future application of this regulatory pathway in man is based on evidence that the human homologue of Qa-1, HLA-E, can function as a restricting element for human regulatory CD8+ T cells. Thus, the studies will provide theoretical basis for clinical application of this regulatory pathway in prevention and treatment of multiple sclerosis in man. [unreadable] [unreadable] [unreadable]